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TARGETING TUMOR CELLS AND MICROVESSELS IN PEDIATRIC BRAIN
TUMORS
by
Jingying Xu
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(NEUROSCIENCE)
December 2010
Copyright 2010 Jingying Xu

Brain tumors represent the most common solid tumor in children and are the leading cause of cancer-related mortality in childhood. Despite modern advances in surgery, radiation, and chemotherapy, a significant proportion of the pediatric brain tumor patients still die of their disease or suffer from poor quality of life. Therefore, more effective and alternative therapies are still in urgent need.; Tumor cell lines derived from central nervous system tumors are critical tools for carrying out preclinical therapeutic testing and studying the biology of the disease. However, to date only few continuous pediatric brain tumor cell lines have been established. The overall aim of the first project was to establish and characterize new pediatric brain tumor cell lines that can be further used for preclinical drug testing and biology study. Here I report the characterization of three new pediatric brain tumor lines: CHLA-200 (anaplastic astrocytoma), CHLA-259 (medulloblastoma) and CHLA-266 (atypical teratoid/rhabdoid tumor). These cell lines are TP53 wide type and show multidrug resistant phenotype, which well-represent what are observed in pediatric brain tumors. CHLA-259 and CHLA-266 were tumorigenic subcutaneously and in brains of NOD/SCID mice, while CHLA-200 was only tumorigenic subcutaneously. These three new cell lines will provide useful models for research of pediatric brain tumors.; Next, we used these novel multidrug resistant pediatric brain tumor cell lines as models for testing of new chemotherapies. We identified novel combinations of ABT-737 with traditional chemotherapies including cyclophosphamide (4-HC), etoposide (ETOP) and topotecan (TPT) as showing significant synergy in killing pediatric brain tumor cell lines in vitro (CI value < 0.3). The combinations synergistically induced apoptosis (TUNEL) and depolarization of mitochondrial membrane potential (JC-1). Apoptosis was associated with decrease in Bcl-2 family members: Bcl-2, Bcl-w and Bcl-XL by ABT-737, and Mcl-1 by 4-HC and ETOP. These findings identify new combinations of ABT-737 and 4HC, ETOP or TPT as combinations that may provide new potential therapy to treat pediatric brain tumors.; Therapies targeting components in the “soil”, especially angiogenesis, have been another attractive strategy in the treatment of pediatric brain tumors. Inhibition of integrins αvβ3 and αvβ5 in human brain microvascular endothelial cells (HBMEC) by the function-blocking peptide RGDfV, an antiangiogenic drug currently in clinical trials (phase II in pediatric brain tumors, phase III in adults with glioma), induces loss of spreading on vitronectin (VN), cell detachment and apoptosis. Latrunculin B (LatB), which inhibits F-actin polymerization, induced transient loss of HBMEC spreading on vitronectin, but not their detachment, and induced apoptosis despite recovery of cell spreading. STI-571 (imatinib), a targeted therapy for BCR-ABL1+ leukemias and inhibitor of c-Abl, PDGFR and c-Kit, decreased endothelial apoptosis. LatB-induced HBMEC apoptosis and its inhibition by STI-571 also occurred in a 3D collagen model, supporting physiological relevance. Last, siRNA to c-Abl (but not nonspecific siRNA) also inhibited RGDfV- and LatB-induced apoptosis. Thus, endogenous c-Abl mediates endothelial apoptosis induced by inhibition of integrins αvβ3/αvβ5 or by LatB-induced disruption of F-actin.

TARGETING TUMOR CELLS AND MICROVESSELS IN PEDIATRIC BRAIN
TUMORS
by
Jingying Xu
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(NEUROSCIENCE)
December 2010
Copyright 2010 Jingying Xu